Process for producing soft magnetic materials

ABSTRACT

A PROCESS FOR PRODUCING SOFT MAGNETIC ALLOYS HAVING IMPROVED CUTTING PROPERTIES TOGETHER WITH THE INTRINSIC MAGNETIC CHARACTERS THEREOF WHICH COMPRISES ADDING AT LEAST ONE OF ELEMENTS OF 0.03-0.30% OF LEAD, 0.03-0.40% OF SELENIUM, 0.01-0.10% OF TELLURIUM, 0.03-0.40% OF BISMUTH AND 0.0010-0.010% OF CALCIUM IN SOFT MAGNETIC ALLOYS WHICH CONTAIN LESS THAN 0.05% OF CARBON, LESS THAN 5.0% OF SILICON, A PART OF SILICON MAY BE REPLACED WITH ALUMINUM, AND THE REMAINDER OF SUBSTANTIALLY IRON WITH OR WITHOUT ELEMENTS FOR IMPROVING MAGNETIC CHARACTERS OF THE ALLOYS, CHARACTERIZED IN THAT MELTING IS EFFECTED UNDER THE FOLLOWING CONDITIONS FOR SATISFYING BOTH INSURMATERIALS AND IMPROVEMENT OF THEIR MACHINABILITIES: (I) HARMFUL ELEMENTS IN MOLTEN IRON SUCH AS CARBON, PHOSPHORUS AND SULFUR OR OXIDES THEREOF ARE REMOVED AS FAR AS POSSIBLE. (II) OXYGEN CONTENT IN THE MOLTEN IRON BEFORE THE ADDITION OF THE ABOVE ELEMENTS FOR IMPROVING MACHINABILITIES IS MAINTAINED AT MOST 200 P.P.M. (III) TEMPERATURE OF MOLTEN IRON AT THE TIME OF THE ABILITES IS HELD AT A TEMPERATURE BETWEEN 1570-1800*C. (IV) THE ALLOYING ELEMENTS FOR IMPROVING MACHINABILITIES ARE ADDED IN THE FORM OF FINE PARTICLES OR LIQUID STATE. (V) THE ALLOYING ELEMENTS FOR IMPROVING MACHINABILITIES ARE ADDED IN MOLTEN IRONS WITH THOROUGHLY STIRRING. NCE OF INTRINSIC MAGNETIC CHARACTERS OF THE SOFT MAGNETIC DDITION OF TH ALLOYING ELEMENTS FOR IMPROVING MACHI

March 27, 1973 PROCESS FOR PRODUCING SOFI MAGNETIC MATERIALS Filed July 10, 1970 CUTTING sPEED /min.)

TWISTING MOMENT AT BREAK TETSUO KATO ETAL 3,723,103

4 Sheets-Sheet 1 23 I 40 h --A 2| [1/3 3o- ,1)

20 o 0 y A 0 I I I l I I 800 900 I000 II00 I200 I300 HEATING TEMPERATURE (C) FIG. I

CUTTING CONDITIONS TEST PIECE A TOOL: SKH4 (HIGH SPEED STEEL) FEED! .I2 /rev. TEST PIECE B DEPTH OF CUT: |.Omm 200 (CONTAINS Pb) (WITHOUT CUTTING LIQUID) 7O I so 30 l I l l l l l l 3 5 I0 20 so 50 I00 200 LIFE OF TOOLS (min)- TETSUO KATO FIG. 2- KATSUSI KUSAKA INVENTORS BY WUQMW ATT NEYS March 27, TETSUQ KATO ET AL. 3,723,103

' PROCESS FOR PRODUCING SOFT MAGNETlC MATERIALS Filed July 10, 1970 I 4 Sheets-Shem 2 S PUNCHING CONDITIONS g TOOL =sI 0II A 6 r n: DIE =DRAFT ANGLE Io E Q PUNCH CREVICE ANGLE 9 5 E PUNCH I '-EDGE ANGLE 9o 9L 2 .5 U 2 g FRONT ABRASION I .4 DIE I- g I r 5 g o.---I sIoE ABRASION Z 9 0 g .2 --9-""- FRONT ABRASION 03 .l h TEST PIECE A2 TEST PIECE s2 (CONTAINS Pb) O I I I l I I o 2 4 s 8 IO I2 NUMBER OF PuNcIIINe (X103) FIG.3'

March 27, 1973 Filed July 10, 1970 CUTTING RESISTANCE (kg/mm N 01 O O TET UO KATO E'TAL PROCESS FOR PRODUCING SOFT MAGNETIC MATERIALS 4 Sheets-Sheet 5 -----TEsT PIECE 0 ---TEST PIECE F (CONTAINS Pb) TEsT PIECE H (CONTAINS Te) CUTTING CONDITIONS FEED: .I2 rev. DEPTH OF CUT: |.2 mm

(WITHOUT CUTTING LIQUID) A.-- TEST PIECE 6 (CONTAINS Se) TOOL: KIO (SUPER HARD METAL) CUTTING SPEED min.)

FIG.4

United States Patent 3,723,103 PROCESS FOR PRODUCING SOFT MAGNETIC MATERIALS Tetsuo Kato and Katsusi Kusaka, Nagoya, Japan, as-

signors to Daido Seiko Kabushiki Kaisha, Nagoya-shi,

Aichi-ken, Japan Filed July 10, 1970, Ser. No. 53,893 Int. Cl. C22c 39/04 U.S. Cl. 75--129 7 Claims ABSTRACT OF THE DISCLOSURE A process for porducing soft magnetic alloys having improved cutting properties together with the intrinsic magnetic characters thereof which comprises adding at least one of elements of 0.03-0.30% of lead, 0.03-0.40% of selenium, 0.01-0.l0% of tellurium, 0.030.40% of bismuth and 0.00100.0l'0% of calcium in soft magnetic alloys which contain less than 0.05% of carbon, less than 5.0% of silicon, a part of silicon may be replaced with aluminum, and the remainder of substantially iron with or without elements for improving magnetic characters of the alloys, characterized in that melting is effected under the following conditions for satisfying both insurance of intrinsic magnetic characters of the soft magnetic materials and improvement of their machinabilities;

(i) Harmful elements in molten iron such as carbon, phosphorus and sulfur or oxides thereof are removed as far as possible.

(ii) Oxygen content in the molten iron before the addition of the above elements for improving machinabilities is maintained at most 200 ppm.

(iii) Temperature of molten iron at the time of the addition of the alloying elements for improving machinabilities is held at a temperature between 15701800 C.

(iv) The alloying elements for improving machinabilities are added in the form of fine particles or liquid state.

(v) The alloying elements for improving machinabilitics are added in molten irons with thoroughly stirring.

The present invention relates to a process for producing soft magnetic materials such as magnetic iron or magnetic silicon steel having improved machinabilities of cutting and punching, in addition to the intrinsic magnetic characters.

Soft magnetic material such as magnetic pure iron and magnetic silicon steel are used in large amounts in electric machineries and various parts such as solenoid iron core, relay, electromagnetic clutch coupling, electric motor, generator and transformer. Recently, demand of soft magnetic materials in automatic controllers and information processors has been increased remarkably.

However, the conventional soft magnetic materials have serious defects of very low processing efiiciencies due to poor machinabilities of cutting and punching owing to their soft, sticky and tough characteristics.

The object of the present invention is to provide a new process for producing soft magnetic materials free from the above defects and having remarkably improved machinabilities of cutting and punching in addition to the intrinsic excellent magnetic characters thereof.

It has already been known that the machinabilities of iron and steel can be extremely improved by incorporating therein lead, selenium, tellurium, bismuth, calcium and the like. However, it has been found that by simply addition of the above elements into the soft magnetic materials, the magnetic properties are decreased and it is difficult to obtain materials having both good magnetic properties and good machinabilities.

The inventors have found in intensive experiments in soft magnetic materials incorporated with the above de- 3,723,103 Patented Mar. 27, 1973 "Ice scribed various elements for improving machinabilities, that those additive elements must be fine particles and homogeneously dispersed through the material in order to obtain both excellent magnetic and machinabilities.

The inventors have also found that the following conditions are required for sufliciently dispersing those additive elements in the materials in the production of soft magnetic materials:

1) Amount of O in melt of iron or silicon steel before addition of elements for improving machinabilities must be kept at most 200 ppm.

(2) Temperature of pure iron or silicon steel at the time of adding additive elements must be held in the range of l570l700 C. in cases of pure iron and silicon steel containing 1% Si and in the range of 1620-1800 in case of silicon steel containing 3% Si.

(3) The addition of additive elements must be carried out under stirring of melted iron or silicon steel by proper means such as gas blowing or electric magnetic induction.

(4) Additive elements must be added in the form of fine particles of diameter of less than 2 mm. or in the molten state.

The process according to the present invention can be applied to magnetic pure iron and magnetic silicon steel of the following standard compositions.

C Si Mn P S Cu Al Pb Pure iron 0. 005-0. 015 0. 20 0. 20 0. 010 0. 015 O. 04 0. 005 0. l5 Silicon steel- 0. 005-0. 015 1-5 0. l0 0. 010 0. 015 0. 04 0. 005 0. 15

Above 0.050% of carbon is unsuitable for soft magnetic alloy due to high coercive force and low magnetic permeability. On the other hand, if carbon content is less than 0.005%, expensive starting materials such as electrolytic iron are required, thus inviting high cost of production. Even pure iron usually contains a very small amount of impurities such as -P, S, Cu and Al and therefore, minimizing only carbon content is not so effective to magnetic properties thereof.

If about 0.20% of silicon is added in pure iron, its coercive force is decreased and magnetic permeability is increased. Thus magnetic characters become excellent and aged deterioration can be prevented. If the presence of a small amount of silicon is allowed, it is advantageous in view of the selection of starting materials and in the 'deoxidation in the course of melting operation. If silicon is incorporated in an amount of about l5%, specific resistance is increased (about 13 iQ-cm.Si percent) and iron loss is reduced.

iManganese have effects for improving hot workability and for preventing brittleness at high temperature caused by sulfur, and this element may be irrconporated generally in an amount of about 0.20%. In such an amount, manganese gives no serious influence upon magnetic character.

Phosphorus, sulfur, copper and aluminium are impurities to be removed as completely as possible, since they will decrease magnetic properties of pure iron and silicon steel. Allowable upper limits of them are as shown above.

Lead, selenium, tellurium, bismuth and calcium are elements usful for improvement of cutting property. Amounts of these elements must be ranged 0.03 030% for Pb, 0.03-0.'40% for Se, 0.01 000% for Te, 0.03 0.40% for Bi and 0.0010.0l% for Ca. If said elements are in amounts above the said upper limits, properties such as magnetic character become inferior.

As described above, it is necessary in the process of the present invention that oxygen content in melt at the time of adding an additive element must be at most about 200 ppm. If the oxygen content is more than 200 p.p.m., magnetic character of the product is inclined to be inferior. For instance, if the content of iron melt is so high as 270 p.p.m., the magnetic properties of the iron will be very poor.

According to the present invention, the temperature of the melt to be added the additive elements is relatively p.p.m. The molten iron was poured in two 700 kg. molds from bottom thereof. The ingots were subjected to hot rolling at about 1200 C. to obtain bars of 60 mm. diameter. Some of the ingots were subjected after the hot rolling to cold rolling and intermediate annealing to obhigher than the temperature in conventional procedure, 5 tain coils having thickness of 1.0 mm. and width of 45 since the higher the temperature of the melt is, the better mm. Chemical compositions of the bars are shown in dispersion of the additive elements will be obtained. The Table 2.

TABLE 2 0 Si M11 P 8 Cu Ni Cr T.Al Pb 0 (p.p.m.)

0. 009 0.13 0. 21 0. 005 0. 00s 0. 07 0. 02 0. 03 go. 002 go. 01 140 0. 009 0.17 0. 22 0. 007 0. 009 0. 05 0. 03 0. 02 0. 002 0.13 155 0. 010 0.17 0.10 0. 007 0. 011 0. 05 0. 02 0. 02 0. 002 0.10 320 temperature of the melt of pure iron as the additive Manganese content of the pure iron was made larger elements being added must be higher than about 1570" than that of ordinary pure irons for the purpose of facili- C. and about 1620 C. for 3% silicon steel. On the other tating hot rolling, and it was confirmed that such an hand, if the temperature of melt is elevated excessively, amount of manganese gives no ill influence to magnetic the tendency of erosion and corrosion of refractories of character. Effects of the addition of manganese on the the furnace will be observed and they also increase imnumber of times of torsion till rupture were as shown in purities in the products or deteriorate magnetic properties FIG. 1. Thus it was confirmed that pure irons having high of the product. Accordingly, desirable temperature for manganese contents have excellent workabilities at a tempure iron is below 1700 C. and for silicon steel contain- 25 perature range of usual hot Working (1200-1000 0). ing 3% of silicon is below 1800 C. A part of the pure iron was used as sample for cutting It is desirable to minimize impurities such as phosphorus test and the remainder was subjected to annealing at a or sulfur in soft magnetic materials of the present inventemperature of 850 C. for 4 hours and cut to rings tion as small as possible. For instance, pure irons con- (inside diameter 33 mm. x outside diameter 45 mm. X taining an appreciate amount of P, S and Pb have the thickness 10 mm.). Magnetic characters of the samples following inferior magnetic properties: were measured. (A and (B in the table show samples in the form of bars having diameter of 60 mm. which P S( P were annealed at 1200 C. for 5 hours in order to imcomivemmflm) L20 M5 M5 prove the magnetic characters. The results of the meas- M11133 6,500 3.000 8,500 35 urement of the magnetic properties of the samples are shown in Table 3. The process of the present invention will be further illustrated in following examples. TABLE 3 EXAMPLE 1 Magnetlc flux dens1ty (gauss) 8105:0112: With use of a 5 ton high frequency induction furnace, B2 B3 (5WD pure iron was prepared from the starting materials shown 13. 000 14.400 15.100 10. 400 0. 75 14.400 14. 900 15.400 10.400 0.00 m Table 13. 000 14.500 15.100 10.400 0.70 TABLE 1 14.500 15. 000 15. 400 10.400 0. 13.100 14.400 15.000 10.400 0. 07 Non-deoxidized pure iron scraps (ton) 1.5 Trimmer (ton) As shown in Table 3, difference in magnetic character Clwpp is hardl obse (1 bet (A) 1 (B) Steel scraps A small amount y we ween pure Irons an Amount of steel scraps was selected so as that the C content in molten steel being 0.009%. After melted, lime and Fe-Si alloy were added therein to control C percent and 0 percent in the molten pure iron to suitable values. Deoxidation-refining by using metallic aluminium is unsuitable in this case, since it gives ill influence to magnetic character of pure iron. After deoxidation-refining with 27 kg. of Fe-Si, oxygen content of the melt as tapping was 110 p.p.m. Then the molten pure iron was taken in a preheated ladle. Temperature of the molten pure iron at that time was 1650 C. Thereafter the molten pure iron in the ladle was directly poured in two 700 kg. molds, and the remainder of the molten iron was charged in an apparatus provided with stirrer and heater. While temperature was kept at 1650 C., the molten iron was stirred. The ladle placed in the apparatus was heated with two graphite electrodes under single phase are. The molten iron was stirred with electromagnetic action induced by electric current. Five minutes after the start of the stirring, 9 kg. of molten metallic lead and small amounts of Ca-Si alloy and metallic manganese were added in the molten pure iron. The ladle was taken out from the said apparatus and the content thereof was poured into two 700 kg. molds from bottom thereof. In the remainder of the molten iron (about 2 t.), 300 kg. of non-deoxidized pure iron were charged and stirred under heating for 2 hours. It was confirmed that oxygen content in the molten iron was 270 which were annealed at magnetic annealing temperature for pure irons, i.e., 850 C. It was confirmed through electron microscope that in pure irons (A and (B annealed at 1200 C., lead was dispersed in fine particles (less than 1 micron) and homogeneously, since a special method of lead addition was adopted, and consequently they are quite stable and not fiocculated in high temperature heat-treatment for controlling crystal grains. On the other hand, magnetic character of pure iron (C) having high oxygen content is very low. Purity after the measurement of magnetic character was observed and it proved that (C) had appreciable amounts of fine silicate impurities and alumina impurities as compared with (A) and (B), and microcracks were observed. It is considered that they have unfavorable effect to the magnetic characters.

FIG. 2 shows lives of high speed steel tools in cutting tests. It is recognized that for Pb-containing pure iron (B) the cutting tool has longer life than for ordinary pure iron (A), in other words, the former is superior to the latter in cutting property. FIG. 3 shows the results of abrasion tests for punching tools wherein die sets of die steel (SKDll) were used. As shown in the drawing, lateral abrasion of the tool in punching Pb-containing pure iron (B) is smaller than that for conventional pure iron (A), but difference is hardly observed between them in front abrasion. For Pb-containing pure iron (C), initial abrasion was high and the tool life was very short.

EXAMPLE 2 In a 5 ton arc furnace, the materials shown in Table 4 and a small amount of lime were charged to prepare pure iron. Then lime, Fe-Si alloy and Al were added therein to control C percent and 0 percent of the molten iron.

L TABLE 4 Press scale 3.0 Trimmer 2.3 Pig iron (metric ton) 0.5

Amounts of Al added were 20 kg. after skimming and 4 kg., before tapping. After deoXidation-refining, but before tapping, 0 content was 90 ppm. Then Ca-Si alloy and metallic manganese were added therein and the molten pure iron was poured into five 1.2 ton ladles. Temperature of the molten pure iron at that time was 1660 C. In three ladles among the five ladles, argon gas was introduced from the bottom to stir the contents therein and lead, selenium and tellurium were introduced through the gas as carrier. Lead was added in one of the remaining two ladles. The molten irons were poured into two 700 kg. molds, respectively, from the top thereof. The temperature of the molten irons at the time of pouring was 1600 C. The ingots thus obtained were subjected to hot rolling in the same manner as in Example 1 to obtain bars having diameter of 60 mm. Chemical compositions of the bars are shown in Table 5.

6 EXAMPLE 3 In a 5 ton arc furnace, materials shown in Table 7 and a small amount of lime were charged, to prepare molten 1% Si-Fe alloy. Then the melt was added with Fe-Si alloy, lime and Al and refined. The molten iron was taken in three 1.5 ton ladles preheated in the same manner as in Example 2, while oxygen content before taping was kept at 120 ppm. and temperature was held at 1690 C. Then a small amount of metallic silicon was added in each ladle to adjust Si content of the alloy. Within two ladles of the three, during pouring the molten iron containing 1% silicon from the arc furnace, lead powder and mixed powder of leadand bismuth-containing materials were introduced in portions just below the flow of the molten iron so as to effect homogeneous dispersion, taking advantage of stirring action of the poured molten alloy.

TABLE 7 Press 2.2

Trimmer 2.0 Pig iron 0.8

Thereafter, the molten alloys were poured respectively in 700 kg. molds from the top of the molds. Temperature of the molten alloys at the time of pouring was 1570 C. Ingots thus obtained were subjected to hot rolling in the same manner as in Example 1 to obtain bars having diameters of 60 mm. Chemical compositions of TABLE 5 Some of the bars were offered as samples for cutting tests and the remainders were subjected to annealing at 9. 9. 000 gamma:

9. 99? coco rommet 9. 5 9 oco 330:.00

the bars are shown in Table 8. The content of manganese of the 1% Si iron is maintained in small amount 850 C. for 4 hours. Then ring samples were prepared so as to prevent formation of fine silicate impurities.

TABLE 8 C Si Mn P S Cu Ni Cr T. A1 Others 0. 017 1.10 0. 07 0. 00s 0. 015 0. 02 0.10 0. 0s 0. 005 0.011 1.05 0. 09 0.001 0.017 0.02 0.08 0. 02 0.012 1310.20 0. 018 1.01 0. 07 0. 010 0. 014 0. 02 0.10 0. 0a 0. 005 51 and magnetic characters thereof were determined. The results of magnetic measurement are shown in Table 6.

TABLE 6 Magnetic flux density (gauss) Coercive force, 0e B1 B2 B3 B5 B05 (oersted) Some of the bars were offered as samples for cutting tests and the remainders were subjected to annealing at 850 C. for 4 hours. Then ring samples (outside diameter 45 mm. x inside diameter 33 mm. x thickness 10 mm.) were prepared and magnetic characters thereof were measured. The results are shown in Table 9.

TABLE 9 Magnetic flux density (gauss) Coercive force, 0e B; B; B (oerstcd) As shown in the above table, no diiference was observed in magnetic flux density of the three alloys, but inferior cooercive forces were observed. Is is found from FIG. 5, which shows the results of measurement on cutting resistance of the three Fe-Si alloys, that Fe-Si alloys containing bismuth and lead have lower cutting resistances as compared with ordinary Fe-Si alloys. In other words, machinabilities of them are excellent.

As described above, machinabilities of a soft magnetic alloy such as pure iron or Si-Fe alloy containing 1% of silicon can be improved without any damage of its intrinsic magnetic character by adding one or more of lead, selenium, tellurium and bismuth in a suitable amount according to a speciad melting method to homogeneously disperse them in fine form. The inventors have further tested on calcium addition in pure iron, Si-Fe alloy and Si-Al-Fe alloy and confirmed that the similar effects can be obtained.

As the result of those experiments, it has been found that there are suitable ranges in amount of additives to be added for improving machinabilities, irrespective of variety of soft magnetic alloys. The lower limit corresponds to a least amount for exhibiting effects of improving machinability and the upper limit corresponds to a least amount for damaging magnetic character of alloy. Preferable ranges of respective alloying elements are as follows:

Percent Lead 0.03-0.30 Selenium 0.03-0.40

Tellurium 0.01-0.10 Bismuth 0.03-0.40 Calcium 0.00100.010

What is claimed is:

1. A process for improving the cutting properties of a soft magnetic steel while maintaining the intrinsic magnetic properties thereof comprising:

(i) preparing molten steel consisting essentially of carbon not more than 0.015%, silicon not more than 0.20%, manganese not more than 0.20%, phosphrous not more than 0.010%, sulfur not more than 0.015%, copper not more than 0.04%, aluminum not more than 0.005% and balance of iron,

(ii) controlling and maintaining the oxygen content in the molten steel at most at 200 p.p.m.,

(iii) holding the temperaturing of molten steel at a temperature between 1570 C. to 1700 C.,

(iv) adding at least one element selected from the group consisting of 0.03-0.30% lead, 0.01-0.10% tellurium, 0.03-0.40% bismuth, and 0.0010-0.010% calcium in the form of particles or in the liquid state into the molten steel under the conditions of (ii) and (iii), with thorough stirring, whereby the cutting properties of the steel are improved without injuring the intrinsic magnetic characteristics thereof.

2. A process for improving the cutting properties of a 8 soft magnetic silicon steel while maintaining the intrinsic magnetic properties thereof comprising:

(i) preparing molten silicon steel consisting essentially of carbon not more than 0.015%, silicon 1 to 5%, manganese not more than 0.10%, phosphorous not more than 0.010%, sulfur not more than 0.015%, copper not more than 0.04%, aluminum not more than 0.005%, lead not more than 0.15% and balance of iron,

(ii) controlling and maintaining the oxygen content in the molten silicon steel at most at 200 p.p.m.,

(iii) holding the temperature of molten silicon steel at a temperature between 1620 C. to 1800 C.,

|( iv) adding at least one element selected from the group consisting of 0.03-0.30% lead, 0.01-10% tellurium, 0.03-0.40% bismuth and 0.0010-0.10% calcium in the form of particles or in the liquid state into the molten silicon steel under the conditions of (ii) and (iii), with thorough stirring, whereby the cutting properties of the steel are improved Without injuring the intrinsic magnetic characteristics thereof.

3. A process according to claim 1, wherein said elements to be added to the melt are added in the form of particles having a diameter less than 2 mm.

4. A process according to claim 2, wherein said elements to be added to the melt are added in the form of particles having a diameter less than 2 mm.

5. A process according to claim 1, wherein said soft magnetic steel contains 0.005 to 0.015% carbon.

6. A process according to claim 2, wherein said soft magnetic silic'on steel contains 0.005 to 0.015% carbon.

7. A process according to claim 2, wherein said magnetic silicon steel contains about 3% silicon.

References Cited UNITED STATES PATENTS 3,438,820 4/1969 Goss 148-110 3,556,873 1/1971 Malagari 123 AA X 3,157,538 11/1964 Imai et al. 148-l10 X 3,305,354 2/1967 Boni ct al. 75-129 3,634,074 1/1972 Ito et a] 75-123 F X HYLAND BIZOT, Primary Examiner J. E. LEGRU, Assistant Examiner U.S. Cl. X.R.

75-123 AA, 123 F, 123 L; 148-3155 

